Proft's Eidetic Memory

When Proft's Eidetic Memory enters, draw a card.
You have no maximum hand size.
At the beginning of combat on your turn, if you've drawn more than one card this turn, put X +1/+1 counters on target creature you control, where X is the number of cards you've drawn this turn minus one.

Murders at Karlov Manor

When Proft's Eidetic Memory enters the battlefield, draw a card.
You have no maximum hand size.
At the beginning of combat on your turn, if you've drawn more than one card this turn, put X +1/+1 counters on target creature you control, where X is the number of cards you've drawn this turn minus one.

Murders at Karlov Manor Promos

If you haven't drawn more than one card by the time a beginning of combat step begins on your turn, Proft's Eidetic Memory's last ability won't trigger at all.

Proft's Eidetic Memory's last ability looks at how many cards you've drawn this turn, even if it wasn't on the battlefield when you drew those cards.

The value of X is determined only once, as Proft's Eidetic Memory's last ability resolves.